iOS is a subset of MacOS. They're not that far apart. Take the A11 chip, triple the amount of cores, up the speed significantly, and add in another GPU and you easily could have desktop class performance*. You have much more cooling to deal with and more power, so it's not a stretch. And while I am not a coder, I imagine that many apps could be ported from Intel to A11 with a click of a button in xcode.
They're not there yet, but could be with a desktop version of this chip. A11x? A11xx? 12 or 24 (6/6 - 12/12) cores + 12 GPU cores running at 3GHz with active cooling? Why not?
* Desktop as in Core i7/9
Because you can just put an AMD threadripper at a fraction of the cost - like tomorrow. And we all already know what happens when you get stuck using a desktop class RISC CPU nobody else gives a crap about.
For what? Sell yourself 4million CPUs a quarter?